Considering the purchase of used TAAS

IMO, I have a gha problem and was talking with someone who uses 1 of your scrubbers and swears by it. So I spent some time and researched your site and was seriously considering the purchase of a scrubber when I happened to find a local reefer that is looking to get out of the hobby and sell his Turbo's algae scrubber.
So, before I take the plunge, what kind of things about the scrubber should I look for or take into account before making this purchase? Age? Model? Lighting?

Also, here is a bit about my setup. I have a 50gal corner with 29gal sump (50gal total water volume). I have crushed coral sandbed, LR, 6 fish, lps, sps, anemones, snail and hermit cuc, carbon, gfo and bio- pellet reactors, ps and rock only refugium which is lit opposite dt lighting. I feed 1 cube mysis/brine 1x day, dose Kalk via ato and my parameter are - alk 8.1, ca 445, mg 1400, P04/N03/NH3&4/N04 are all 0ppm. My lighting is led and on a ramp up/dn 12hrs day with max lighting for 4hrs.

Using an ATS should help to control GHA by having the algae grow on the scrubber instead of in your display tank.

results vary of course, depending on your tank and setup. I had a gha outbreak 6 months ago. Still fighting it with a combination of reduced lighting hours in the display tank, using an ATS and raising Mg.

The L2 would do well on a 50g setup with that level of feeding. Any of the models work fine, the older "Rev 1" L2 used plain heat sinks from HeatSinkUSA (vertically oriented) so that is how you can tell those units apart. The Rev 2 uses MakersLED heat sinks (horizontally oriented) and has the U-shaped cutouts for cradling the slot pipe (same as Rev 1). The Rev 3 has threaded connections for the slot pipe and drains, so that one is slightly different looking.

If you can message me with who you are looking at buying it from I can tell you which model it is. Also the warranty and support transfers, but that's only useful when the buyer knows to contact me, so you're ahead of the game there!

Upgrade kits are also available and I can make recommendations for which ones I think would benefit you the most, depending on the unit. Rev 1 L2s are good as is except the slot pipe is saw-cut Schedule 40 and I use router-cut schedule 80 now, it's a cheap upgrade ($10), and I would send you light blockers to add also (those alone would be free)

The GHA issue could be a result of many things, but you are sure attacking it from almost every angle at this point - CUC, pellets, skimmer, carbon, GFO, adding the scrubber would round it out and if that doesn't do the trick I would be surprised!